Manufacture of low boiling tar acids



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Patented Apr.'18, 1933 TTEIS SOLOMON CAPLAN OF BROOKLYN, NEW YORK,ASSIGNOR TO COMBUSTION UTILITIES PATENT OFFICE CORPORATION, OF YORK, N.Y., A CORPORATION OF MAINE MANUFACTURE-00F Low BOILING TAR Aoins Thepresent invention relates to the production of low boiling tar acids,and more particularly to a process for converting high boiling tar acidsof-relatively low marketable value into low boiling tar acids of highermarketable value.

Low temperature tars and similar products such as blast furnace'andvertical retort tars are characterized by having a high content ofrelatively high boiling phenolic or phenollike bodies to which the termtar acids is generally applied. There is no appreciable present marketvalue for these high boiling tar acids per se, whereas there is animmediate and profitable market for low boiling tar acids, notablyphenol and the cresols, which are present in small quantities in cokeoven tars and similar condensates obtained by the high temperaturedistilation of coals and the like.

The primary object of the present invention is to provide a process fortreating the high boiling tar acids of low temperature and primary tarorigin to increase their market value.

With this object in View one feature of the invention contemplatesconverting such high boiling tar acids to low boiling tar acids such asphenol and cresols.

Heretofore it has been proposed to effect the reduction of high boilingtar acids of the class above referred to, to the lower boiling taracids, by contacting a spray of the tar acids with a current of hydrogenin a highly heated tube, the hydrogen being obtained either from anexternal supply orelse by interaction of steam with iron or carbonwithin the hot tube. It has also been proposed to use catalysts such asnickel or activated carbon in conjunction with the hydrogen reduction ofthe tar acids. This latter method of treatment however, wherein hydrogenis caused to react with the higher boiling tar acids in the presence ofcatalysts, is not at all satisfactory in the matter of yields of thelower boiling phenols, the major portion of the recovered productsconsisting of low boiling hydrocarbons such as benzene and toluene.Moreover, the use of catalysts involves considerable expense for therea- Applicatien filed. September 29, 1926. Serial No. 138,571.

son that all commercial tar acids contain appreciable quantities ofsulphur compounds, and such sulphur compounds quickly poison anycatalyst which is used in the reducing chamber, with the result that thecatalyst has to be renewed very frequently.

Accordingly another object of the present invention is to provide a.process by which high boiling tar acids of the character referred to maybe cheaply and substantially completely converted into valuable lowboiling tar acids.

With these and other objects and features in view the invention consistsin the process for producing low boiling tar acids hereinafter describedand particularly defined in the claims.

Essentially'the process for producing low boiling tar acids forming thesubject of the present invention, in its preferred form, consists inpassing the vapors of high boil ing tar acids together with an excess ofsteam through a reaction tube containing no catalyst and having nocatalytic effect, the tube being heated to a temperature between 600 and800-C., preferably about 650 0., and the time, contact, and otherreaction conditions being so regulated as to effect the conversionpreferably of at least 90% of the original high boiling tar acids intovaluable low boiling tar acids.

The following procedure is set forth as an example of a method oftreatment which has been found entirely satisfactory: A tar acidfraction of low temperature tar consisting mainly of Xylenols wasdistilled by means of a current of steam through asilica tube heated byan electric furnace so that the temperature inside the tube registered650 C. About three parts by weight of steam were used'for every part oftar acids. The liquid products obtained on condensation of the reactionvapors were analyzedand found to contain a mixture of phenol andcresols. The yield of the low boiling tar acids produced was found tocomprise 94.3% of thecalculated theoretical yield of cresols obtainablefrom the original volume of xylenols taking part in the reaction. Theprocess has also been applied to the treatment of low'temperature tardistillates containing hydrocarbon oils and nitrogen bases in admixturewith high boiling tar acids, so that the process is not limited in itsapplication to the treatment of tar acids alone, but may be employed ifdesired in the direct fractional distillation of oils containing suchhigh boiling tar acids, with the object of recovering the tar acidcontent in a converted low boiling form.

As previously mentioned, prior experimenters on the conversion of highboiling to low boiling tar acids have all employed hy-.

drogen as the reducing agent by which to split ofl the alkyl groups fromthe high boiling tar acids and thereby convert the high boiling taracids into lower boiling phenols. Experiments have shown, however, thathydrogen is not a satisfactory agent to employ for carrying out theconversion, and the reason that hydrogen has not proven to be the bestagent for this purpose is thought to be demonstrated by the followingconsideration of the equilibria involved in the various reactions takingplace in the conversion chamber. There are apparently two main reactionstaking place when hydrogen and tar acid vapors are mixed at an elevatedtemperature. In one of these reactions the hydroxyl group of the taracids is split out and immediately combines with the hydrogen to formwater, the tar acids being thus con verted into hydrocarbons. In theother principal reaction the alkyl side chains are split out from thetar acid and combine with the hydrogen to form gases, the tar acidsbeing thus reduced tothe lower boiling phenols. These two reactions maybe expressed as follows, the higher boiling tar acids being representedas xylenols C H (CH OH, and the lower boiling phenol products of theconversion being represented as cresols C ILCI-LOH.

1- OGHg 20H H2 C IL (CTI 2 I1 0 2. 0 11 (CH 0H H,

The reaction designated as (1) above is undesirable since it leads to aproduction of hydrocarbons instead of to the production of valuable lowboiling phenols such as are produced by reaction (2). It is thought thatthe greater yields of low boiling tar acids which are obtained by thepresent method over the former proposed methods of produc- 111g highboiling tar acids by means of hydrogen may be explained by aconsideration of the law of mass action. Thus it is believed that anapplication of the law of mass action to the reaction (1) above willshow that this undesirable reaction would be retarded by the presence ofa large molar excess 9f steam in the reaction chamber. since steam 1sone of the two products of the reaction. B37 employing steam in place ofhydr g n and by carrying out the conversion reactions at a temperaturefar below the lowest temperature at which decomposition of steam takesplace and in the absence of any catalyst for such decomposition,reaction (1) is entirely avoided by the process of the presentinvention. Experiments carried out in connection with the presentinvention have shown that steam at temperatures between 600 and800 C.and in the entire absence of catalysts is as suitable an agent ashydrogen for causing the splitting off of the alkyl side chains fromhigh boiling tar acids, as expressed in reaction (2) above. Thus thereaction taking place when steam rather than hydrogen is employed as thedealkylating agent may be represented as follows:

Any tendency of the hydrogen which is produced in this reaction to enterinto reaction with the hydroxyl group of the tar acids in accordancewith the reaction (1) to produce hydrocarbons is greatly retarded, ifnot entirely inhibited, by the presence of the large molar excess ofsteam in the reaction chamber, as explained above. In fact it 1sbelieved that the production of hydrocarbons, as in reaction (1) above,is entirely eliminated in carrying out the preferred planof the presentinvention at temperatures n the neighborhood of 650 C., for experimentshave shown that reaction (1) above proceeds very slowly at temperaturesbelow 700 C., in the absence of catalysts. I

In order that the steam may not react with the walls of the hot reactiontube, with consequent conversion into hydrogen, it is preferred to usematerials in the construction of the hot tube which are inert towardsteam and which also will not act as catalysts for the undesirablereactions resulting in the production of hydrocarbons by reduction ofthe high boiling tar acids. The reaction tubes may be constructed eitherof a material, such as fused silica or porcelain, which is inert towardssuperheated steam, tar acid vapor. and their conversion products, orelse the tubes may be constructed of some material which becomes quicklycoated with a stable film on contact with air or steam at elevatedtemperatures. and becomes thereafter inert toward superheated steam, taracid vapors, and their conversion products. As an example of the secondclass of materials mentioned above aluminum may be cited. On heating inair or steam aluminum becomes coated with a very stable film of oxidewhich is inert towards the steam and the tar acids and their conversionproducts. Aluminum. however, is not a satisfactory material for use inmaking up the reaction tubes employed in accordance with the process ofthe present invention, because of its low fusion point.

Calorized iron on the other hand (specifically iron having a coating of.aluminum) behaves in the same manner on heating in the presence of airor steam as does aluminum, and has been found to be a very satisfactorymaterial for use in making up the reaction tube. There are, undoubtedly,other materials which are equally as satisfactory as calorized iron inthe respects mentioned above.

Another advantage which should be noted as directly resulting from theuse of steam in effecting the reduction of high boiling tar acids isthat it serves to prevent any deposition of carbon in the hot reactiontube, such as might occur in the absence of steam through completedecomposition of some of the tar acids. Thus when tar acids alone, inthe absence of steam, are passed through a hot tube, a considerableamount of cracking of the tar acid molecule takes place with resultantdeposition of carbon and the formation of some low boiling hydrocarbons.It has been known for some time that if small quantities of steam areintroduced into a hot tube wherein cracking reactions are promoted, thedeposition of carbon is thereby prevented. However, so far as known, allprior processes for producing low boiling tar acids from high boilingtar acids are based primarily on thermal decomposition of the tar acidmolecules, the resulting products consisting almost entirely ofhydrocarbons with only small amounts of low boiling phenols. Accordingto the process forming the basis of the present invention, on the otherhand, a large molar excess of steam is employed. Thereby the tar acidsare protected from thermal decomposition and the steam and tar acidmolecules interact chemically in accordance with stoichiometric laws toproduce substantially quantitative yields of low boiling phenols andsubstantially no hydrocarbon products.

It is not intended that the above description shall be construed aslimiting the invention in its scope or application to the use of any onetemperature or of any one rat-i0 of steam to tar acids, nor to thetreatment of any particular fraction or group of tar acids, nor to anyparticular method of efi'ecting the introduction of the tar acids andsteam into the heated reaction tube. Thus although steam distillationwas employed in treating the high boiling tar acids in the particularapplication of the invention cited as an example, any other method forintroducing the tar acids and steam into the heated reaction tube may beemployed, such for example as that of spraying the tar acids by means ofa steam injector into the tube.

The term tar acids is used in the description and claims as a genericterm to define all alkali-soluble hydroxy derivatives of aromatic andnonaromatic cyclic hydroresemble the phenols, cresols and the -phe-'nolic homologues of coke oven tar in some of their properties, do notcome within the generally accepted definition of a phenol but are ratherhydroxyl derivatives of cyclic hyv drocarbons which are nonaromatic incharacter, having hydrogen and alkyl side chains attached to the cyclicnucleus.

The preferred form of the invention having been thus described, what isclaimed-as new'is: Y

'1. The process for converting high boiling tar acids into 'tar acids oflower boiling point, which comprises contacting vapors'of the formerwith a large molar excessv of steamat an elevated temperature rangingfrom1600'C. to 800 (3., adapted to facilitate the said conversionreactions, .in the absence of solid materials reacting with steam togenerate hydrogen, and collecting the re action products. I

2. A process for converting high'boiling tar acids into tar acids oflower boiling point which comprises passing a mixture of vapors of saidhigh boiling tar acids and superheated steam'through a reaction zone ata temperature between 600 and 800 C. in the absence of materialsreacting with steam to generate hydrogen.

3. The process for converting'high boiling tar acids intotar acids oflower boiling point, which comprises contacting vapors of the highboiling tar acids with a molar excess of steam at an elevatedtemperature below 800 C. to cause conversion of the high boiling taracids and to produce tar acids of lower boiling point withoutsubstantial conversion of the former to hydrocarbon products, the saidconversion being conducted in the absence of catalysts adapted tofacilitate hydrogenation reductions.

4. The process for converting high boiling tar acids into tar acids oflower boiling point, which comprises passing a mixture of vapors of thehigh boiling tar acids and steam through an independently heatedunobstructed reaction chamber maintained at an elevated temperature nothigher than 800 C. but sufliciently high to cause the conversionreactions to occur between the components of the mixture and to producetar acids of lower boiling point, the inner surfaces of the reactionchamber in contact with the vapor mixture being made of a material whichis nonreactive with superheated steam to generate hydrogen at thetemperatures employed.

5. A process for converting high boiling tar acids into tar acids oflower boiling point which comprises passing a mixture of about one partby weight of the vapors of the high boiling tar acids and about threeparts by weight of steam through a reaction zone heated to a temperaturein the neighborhood of 650 C. in the absence of iron, and condensing andcollecting the mixture of vapors leaving said reaction zone.

6. The process of treating low temperature tar distillates containinghigh boiling tar acids which comprises vaporizing the said distillateand contacting the vapors thereof with steam in amount by weight greaterthan the amount of high boiling tar acids present in the said distillatewhile maintaining an elevated temperature between 600 C. and 800 0., inthe absence of any catalyst adapted to facilitate decomposition of thesteam to form hydrogen at the temperatures employed.

, 7. The process of converting high-boiling tar acids into tar acids oflower boiling point which comprises, injecting vapors of the former witha molar excess of steam into a reaction zone maintained at a temperatureof from 600 C. to 800 0., which zone is free of solid materials adaptedto react with steam to generate hydrogen, and collecting the reactionproducts.

8. The process for converting high-boiling tar acids into tar acids oflower boiling point which comprises, passing a mixture of vapors of thesaid high-boiling tar acids and a molar excess of steam through areaction zone maintained at a temperature within the range 600 C. to 700C., in the absence of solid materials capable of reacting with steam atthe said temperature to generate hydrogen.

In testimony whereof I afiix my signature.

SOLOMON OAPLAN.

